Xyloglucans have been found to be an important factor in cell wall morphogenesis (reviewed in Baumann et al., 2007) and are able to make hydrogen bonds to cellulose, for reference see The Plant Journal, 1993, p. 1-30.
Polysaccharide transglycosylases, also called polysaccharide transglycanases, catalyze the reorganization of polysaccharide molecules by cleaving glycosidic linkages in polysaccharide chains and transferring their cleaved portions to hydroxyl groups at non-reducing residues of other polysaccharide or oligosaccharide molecules (reviewed by Franková and Fry, 2013; herewith incorporated by reference). Examples of transglycosylases are transglucosylases (also called transglucanases), transxylanases and transmannanases. Of these, Xyloglucan endotransglucosylases (XETs; also called xyloglucan endotransglucanases, or XTHs or xyloglucan xyloglucosyl transferases) restructure xyloglucan in primary and secondary cell walls of land plants including Equisetum and liverworts (Fry et al., 1992; Fry et al. 2008). Unlike most other land plants tested, Equisetum additionally exhibits a distinct endotransglucosylase (or endotransglucanase) called mixed-linkage beta-glucan:xyloglucan endotransglucosylase (MXE) (or mixed-linkage beta-glucan:xyloblucan endotransglucanase). The latter enzyme uses mixed-linkage (1,3;1,4)-beta-glucan (MLG) as the donor substrate and attaches it covalently to xyloglucan or a fragment thereof (Fry et al., 2008). So far, enzymes catalyzing hetero transglycosylation, i. e. using qualitatively different donor and acceptor substrates, have been found but not characterized in detail (Ait Mohand and Farkaš, 2006), or have been found to only have a minor hetero-transglycosylation activity (Hrmova et al., see below).
It has been shown that xyloglucans are covalently linked to pectic polysaccharides (Thompson and Fry 2000). Evidence for covalent linkage between xyloglucan and acidic pectins in suspension-cultured rose cells is described in Abdel-Massih et al. (2003) and Cumming et al. (2005,). Furthermore, Hrmova et al. have shown that an XET from barley links MLG, hydroxyethylcellulose and sulfuric acid swollen cellulose (i. e. cellulose sulfate) to xyloglucan (Hrmova et al. 2007). In its capacity to link MLG to xyloglucan, this barley enzyme exhibits MXE activity which, however, amounts only to about 0.2% of its XET activity.